Re: [Qemu-devel] nested VMX with IA32_FEATURE_CONTROL MSR(addr: 0x3a) value of ZERO

[Paolo Bonzini]

On 13/01/2015 14:19, Huaicheng Li wrote:
> Hi, all
> 
> I have a Linux 3.8 kernel (host) and run QEMU 1.5.3 on it. I want to
> test another hypervisor software in qemu so I enabled KVM's nested VMX
> function(by passing "nested=1" parameter to the kvm module) and then
> started a guest machine. In the guest, I could see the "vmx" instruction
> set by reading /proc/cpuinfo and the kvm module can be correctly
> inserted. But when I read the value of the IA32_FEATURE_CONTROL MSR
> using msr-tools, it showed _0_, but the correct value should be _5_,
> since bit 0(virtualization lock bit) and bit 2 of that MSR must be set
> to enable the virtualization functionality. But in my vmware workstation
> guest with nested virtualization enabled, the value of that MSR is,
> indeed, _5_ as well as in the physical machine (of course). Here, I want
> to ask
> 
> * Am I missing anything in my operation to totally enable the nested
> virtualization function ?? (I googled a lot and it seemed there were no
> additional steps) 

You have an old kernel.  IA32_FEATURE_CONTROL MSR emulation was added in
3.12.

> * Since the IA32_FEATURE_CONTROL MSR value should be set in BIOS and are
> kept unchanged during the runtime, is there any modified BIOS that qemu
> can use to enable the setting ?? Currently my qemu use the default one.

This is a bug in your hypervisor.  It should be ready to set bit 0 and
optionally bit 2 of IA32_FEATURE_CONTROL, if it sees
IA32_FEATURE_CONTROL = 0.

Paolo